An ignitron is a known device used for switching large currents in which a pool of liquid mercury acts as a cathode. An ignitor is used to establish an initial discharge between the mercury cathode and the ignitor. The initial discharge then enables the main arc between the anode and the mercury cathode to be struck and hence allow conduction through the switch.
The present invention arose from considering a switch arrangement capable of conducting large amounts of charge and high currents without requiring the use of mercury.